Explosion forming process



Dec. 6, 1966 E. AMlNx ETAL 3,289,447

EXPLOSION FORMING PROCESS Filed Aug. 8, 1963 4 Sheecs-Sheefl l HMIH HHH

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Hummm? mmm HIl l Dec. 6, 1966 E. AMlNl ETAI. 3,289,447

EXPLOSION FORMING PROCESS Filed Aug. 8, 1963 4 Sheets-Sheet 2 Dec. 6, 1966 E. AMINI ETAL.

EXPLOSION FORMING PRocEss 4 Sheets-Sheet 5 Filed Aug. 8, 1963 Dec. 6, 1966 Filed Aug. 8, 1963 E. AMINI ETAL EXPLOSION FORMING PROCESS 4 Sheets-Sheet 4 WGA.

United States Patent O 3,289,447 EXPLGSHUN FRMNG PRWCESS Ehssanollah Amini, Sutton Coldheld, and Stephen Aihert Tobias, Birmingham, England, assignors to National Research Development Corporation, London, England, a British corporation Filed Aug. 8, 1963, Ser. No. 3%,749 Claims priority, application Great Britain, Aug. 9, 1962, 30,600/62 l tlaiins. (Cl. 72-56) This invention relates to the explosion-forming of materials, and particularly of sheet metal.

Much work has been done in developing techniques for this process in which intense shock waves produced by detonation of an explosive charge cause deformation of a workpiece, which can involve the shaping of sheet metal or consolidation of material, possibly a metal powder compact. The pressure pulse resulting from the detonation is of short duration and the peak pressure on the workpiece, besides depending upon the size of the charge, depends upon the distance of the charge from the workpiece; but the greater the distance, although the peak pressure will be less, the longer is the duration of the pulse. Also, the shape of the pulse front will depend not only on the size and geometry of the charge, on the presence or otherwise of a reflector behind the charge but also on characteristics of the intervening medium. lt is found that the pressure distribution is better the more incompressible the medium; so that best results are usually obtained it the medium is a liquid, and for this reason such processes have normally been carried out in a water tank.

lf only for the reasons that these processes tend to be noisy and that much scattering of water results, it has been usual to carry them out in the open and they have not been developed as widely industrially as is feasible, Proposals have been made to contain the explosion in a closed space. It is an object of the present invention to provide and improve such apparatus.

In accordance with the invention an explosion-forming apparatus comprises a workpiece-retaining part, a pressure-pulse-shaping part which is internally proled to determine, in association with explosive positioning means, the shape of the pulse reaching a workpiece, and means for ensuring pressure-tight connection between the two said parts to form a substantially totally enclosed chamber.

Thus the pulse-shaping part may be profiled to approximate to a parabola, and the explosive-positioning means may be arranged to place the explosive at or near the focus of the parabola, or the positioning means may be adjustable to provide different pressure pulse shapes.

Examples of sheet metal forming apparatus which embody the invention will now be described with reference to the accompanying drawings of which FIGURE l shows a central section through the apparatus; FIGURE 2 shows a central section through another apparatus which is particularly well adapted for use, for semi-automatic or automatic operation in a system as illustrated diagrammatically in FIGURE FGURE 3 gives a more detailed, scrap view of the part labelled A in FIGURE 2, and FIGURE 4 is a fragmentary, sections l view of the part labelled B.

In FIGURE 1 the work-retaining part ll is shown as a clamping plate 2 to which the workpiece 3 (here a circular plate) is clamped by a ring 4 and the clamping plate provides also a guide surface on which the sheet metal is to be deformed. Gf course dies may be provided, it required. The bottom ot the forming compartment is sealed by a plate 5 and la connection is made, through the aperture 6, to a vacuum pump, so that the impulsed movement of the metal into the forming space ICC shall not be impeded. Provided that there is some form of flange, possibly flexible, against which the workpiece can be positioned, there may be circumstances in which there is no necessity for the workpiece to be positively clamped to the workpiece-retaining part; and for this purpose the force on the workpiece caused by evacuation of the forming compartment may suce to hold the workpiece in position against the ilange pending ring of the explosive. The pulse-shaping part 7 comprises a casting 3, possibly of concrete, having its internal surface profiled roughly to parabolic shape as shown. The cast-ing is secured to a top member 9 by which it can be lifted away from the lower part 2l, or alternatively retained while the lower part is lowered therefrom. An explosive charge 10 is arranged to be supported by the tiring mechanism 11, in which a firing pin l2 for the charge may be loaded by the spring 13 and held by the release plate 14 which is normally locked by the safety screw l5. The tiring mechanism may be made readily movable through the top member 9.

In use, when the workpiece has been clamped in position, the two parts are brought together and sealed by the O-ring 16, die-bolts 17 distributed round the circumference clamping them in the sealed condition. Water is then run in to till the space between the workpiece and the top part, for which purpose the hole left when the tiring mechanism is withdrawn, may be used. The charge -is adjusted to be in the best position for the detonation required; it can then be fired and the pressurised gases released from the explosion produce the required shaping, thereafter the parts are separated for removal of the shaped workpiece.

Provision may be made to re the charge electrically, for instance either using electrical detonators, or a solenoid to impact on the firing pin, Also, the steps of loading, clamping and releasing the workpiece; the raising and lowering of the top part; the llinfJr and emptying of water; and the loading of the explosive charge and removal of the spent charge, may all be made automatic.

The arrangements for feeding and clamping the workpiece may be such that a hopper may be used, or alternatively a strip which can be fed in from a reel of material. lso it may be necessary that more than one charge should be tired, possibly automatically until the deformation is completed. Further arrangements may be made for automatic ejection of finished workpieces.

Advantages of the apparatus described with reference to FlGURE l appear to be as follows. Thus, because the explosion is contained within a closed cavity, very little noise can be heard in the vicinity of the apparatus; and by suitably shaping the profile of the upper part, and/ or by suitably positioning the charge, it is possible to distribute the pressure front over the whole area of the workpiece or to concentrate it in one or more zones of the area for higher -utilizatin of the energy of detonation.

A still `more advantageous arrangement is indicated in FIGURES 2 4. In those figures, a pulse-shaping part has a traine 2l fabricated from sheet metal with strengthening ribs 22 at intervals around it, concrete lling the spaces between the ribs and having a reasonably smooth surface 23 ot' substantially parabolic section.

The frame 2l is supported, with the surface 23 facing upwards, on three legs 24 upon which it is seated for easy removal, by means of 'bosses 25 with securing bolts 26.

The charge-positioning means comprises a head 27 mounted on a piston 28 which is moved up and down by means of an hydraulic cylinder 29, the head being shown in its yoperative position in FIGURE 2, but without a charge. The head 27 carries a sleeve 34B which slides in a bearing 3l bolted to the frame 2l, the lower end of the sleeve having a steadying ange 32 which is provided with a projection 33 sliding in a slot 34 in the protective cover 355 surrounding the charge-positioning gear. The effect of the groove 34 is to prevent rotation of the sleeve 3l when the sleeve is ybeing moved.

The frame 2l is also formed with a chamber 36 which communicates by means of the pipe 3S with a gate valve 39 in a water supply line 4@ to supply water to the pulsetransmitting space.

A workpiece 42 is arranged to be clamped against a backing and forming member 43, between an orice member 44 on the ange 45 ofthe frame 21 and the flange 46 of the retaining part 47. The air -in the space within the part 47, behind the workpiece, is arranged to be evacuated by means of a vacuum pump connected to the outlet `43. The arrangements for clamping the parts of the apparatus together at the flanges 45 .and 46, comprise a number of h', draulic clamps 49 spaced around the circumference at 45 spacings. Each clamp comprises a piston 50 having a projection l passing through a hole in the flange 45. Piston 50 is provided with an end ange 52, the piston being operated by an hydraulic fluid cylinder 53 The ange 4S has holes 55 which permit the franges 52 to pass through the flange 4S when the part 47 is moved relative to the part `4l, and for clamping purposes, a wedge member 56 is arranged at each clamp to be moved into position by means of an hydraulic gear 57 or of a pneumatic means; the withdrawn position of the wedge member S6 is also indicated at S651 in FIGURE 3.

Referring now to FIGURE 4, the charge retaining member or holder 58, which may advantageously be formed from a rubber or other relatively pliable insulating material, is shown in position on the head 27, a spigot 69 positioning the retaining member. This head 27, which is of insulating material, carries collet operating means 59 and 6i), collets 6I and 62 `being adapted to engage the leads 63 and 64 respectively from the charge 65, to make electrical connection to a suitable ring circuit. The collets 6l and 62 are carried by a member 66 which is biased away from the head 27, by means of springs 67, 68 so that, in the lining position of the charge, the piston 28 draws the the member 66, and therefore the collets 61, 62 downwards to close them on the charge leads under the action of the springs 67, `68.

It will be observed that the retaining member 58 is shaped to embrace the ends of the collets 6l, 62 to protect them from any debris emanating from the charge when exploding or the member maybe of larger form if necessary, to cover the whole of the end of the bearing 3l for .a similar reason.

In operation, after a charge has been tired and the retaining part 4'7 lifted away to enable the shaped workpiece to be removed, the piston 28 is operated to raise the member 66, thereby releasing the collets and, after engagement with the head 27 raising the spent charge through the water in the pulse-shaping space above the level of the flange 45. When in this position the spent charge, iin .its retaining member 53, is exposed for removal by an yoperator who will replace it by .a further charge assembled on its retaining member. Thereafter the piston 23 is retracted and the fresh charge is drawn down into position, the collets 6l and 62 engaging its leads.

It `will probably be necessary to discard the retaining member after the explosion, since it is almost certainly to he affected yby the force of the explosion and a fresh retaining Imember will need to be provided for each operation.

It is preferably arranged, for safety purposes, that electrical contact to the charge from the tiring circuit is not completed until the piston 2S has retracted the head 27 into its operative tiring position. Thus the ange 32 on the sleeve 30 may be arranged to operate contacts, such as in a micro-switch (not shown) when reaching its fully retracted position.

Referring now to FIGURE 5, a convenient arrangement is shown, for use, for mainly automatic operation, on a production line basis. Here two workpiece retaining parts 47a and 47]? lare provided for a common pulse-shaping 4 part 41. These two parts 47a, 47h are mounted on either end of an arm 7G arranged to be rotated labout an axis 7l, there being four stations for each part 47a and 47h `in a complete cycle.

At the rst station, with arm 7 0 on the line I, the part 4712 receives a workpiece which is accepted from a sultable holder or hopper 72 of blanks; the simplest arrangement will be that in which the fresh blank is sucked up on to the workpiece-retaining part by evacuating the space behind the workpiece, and this evacuating operation may serve lalso as preparing the part for the forming operation. Alternatively the workpiece may be punched from a strip 73 and the punching 'action may be carried out by operation of the arm itself. At the same time, the other part 47a retains its own workpiece in position on the pulse-shaping part 41 for forming. After the forming operation on the workpiece in 47a is completed and the new workpiece has been accepted onto part 47b, the larm 70 is raised to free the parts 47a and 47b from the respective co-operating parts, and is rotated to the position indicated in dotted outline on the line II, where part 47a releases its formed workpiece, for example onto a conveyor 74 for conveyance to a hopper 75, or for other disposal as required. In this position, in which the part 47!) is at its second station, any further necessary preparatory operation may be performed on the apparatus or the workpiece, the part 41 being left clear for an operator to exchange the spent charge for a fresh charge, the charge positioning head having been 4arranged to be raised to its exposed position during this movement of the arm 70.

The fresh charge having been placed in the charge head, and the formed workpiece having been removed, the arm 7@ may be rotated so that part 47h is brought over the pulse-shaping part 41, the charge head being drawn down into its operative position during this part of the rotation. When the arm 70 has been lowered to bring the part 471; into the engaging position for the hydraulic clamps S3 to be operated and for the part 47a to receive another workpiece, the forming operation may be carried out on the new workpiece and the cycle repeated. The dimensions of the parts will be such as to cope with the particular thickness of the workpiece, it being clear that for the thicker workpieces it may be necessary to make the pulseshaping profile part of other than fabricated form to cope with the pressures involved.

It will be appreciated that the cycle that has been described may be 4almost entirely automated; in fact, even the spent-charge-removal/fresh-charge-replacement operation may be made automatic. Of course, some manual labour will almost inevitably be involved in assembling and charge-retaining members, since the assembly operation involves threading the lead wires through suitable holes in the retaining part 5S, shaping the ends of the lead wires to mate with the collets, and also ensuring that these ends are such that they can be fed easily into the respective collets. It is possible, however, that even these operations may be automated. Alternatively charge assemblies may be prepared at the explosives factory which supplies the charges.

An additional advantage of the arrangement described, in association with the clamping arrangement of FIG- URES 2 and 3 is that the complete cycle time may be made reasonably short and will be useful for mass production applications.

It is to be understood that apparatus in accordance with the invention may have a pulse-shaping part adapted to provide a pulse form of a more complicated material than described above; thus the pulse-shaping part may be shaped to co-operate with a plurality of explosive charges and, for this purpose, it may be necessary for the prole to be re-entrant in a number of places. The actual profile to be adopted in any particular case would appear to be dictated to a certain extent by the deformation that is required to be imparted to the workpiece.

We claim:

1. An explosion-forming apparatus for performing a forming operation on a workpiece, comprising a pressurepulse-shaping part, said pulse-shaping part being arranged to face upwardly so as to retain liquid for pulse transmitting purposes, a workpiece-retaining part, said workpieceretaining part being arranged for substantially pressuretight connection to said pulse-shaping part, an explosivepositioning means associated with said pulse-shaping part, extension means for said explosive-positioning means, said extension means being arranged to extend said explosivepositioning means from its operative position within said pulse-shaping part to be positioned such that a spent charge may be removed and to be replaced by a fresh charge, for retraction into its operative position.

2. An explosion-forming apparatus as claimed in claim 1, wherein means for extending said explosive-positioning means is adapted to co-operate with contact means to prevent completion of the ring circuit for said explosive at least until the work-retaining part is in position, and the explosive has been correctly positioned.

3. An explosion forming apparatus as claimed in claim 1, wherein a sealed bearing for said extension means is provided on the axis of said proled part.

4. An explosion forming apparatus as claimed in claim 3, wherein means for receiving leads from the detector for the explosive `are provided on said explosive-positioning means and said extension means comprise a lost-motion device, said lost-motion device being adapted to cause operation of contact means in a tiring circuit for the explosive, whereby completion `of said ring circuit is prevented before the explosive positioning means is in its operative position.

'5. An apparatus for explosively forming a workpiece which comprises: a pressure-pulse-shaping part delining a wave-shaping cavity which is open at one end, said part being disposed with the open end of said cavity facing upwardly so as to retain liquid for pulse transmitting purposes; conduit means for withdrawing liquid from said cavity, said conduit means extending downwardly from the lowest point in said cavity; explosive-positioning means associated with said shaping part for positioning an explosive in said cavity; a workpiece-retaining part arranged above said shaping part, said retaining part being engageable with said shaping part so as to locate a Workpiece opposite the open end of said cavity; and releasable clamping means for clamping said shaping part and said retaining part together in pressure-tight relationship.

6. An -apparatus for explosively forming a plurality of workpieces which comprises: at least two workpiece-retaining parts; a pressure-pulse-shaping part defining a wave-shaping cavity which is open at one end; means for sequentially aligning each of said workpiece-retaining parts with the open end of said cavity, said means including a mounting member carrying said workpiece-retaining parts in spaced apart relationship to each other, said mounting member being movable to a first forming positioning in which one of said workpiece-retaining parts is aligned with said cavity to a second forming position in which the other of said workpiece-retaining parts is aligned with said cavity and to at least one intermediate position in which neither of said workpiece-retaining parts is aligned with said cavity; means fixing said Wave-shaping part against disaligning movement relative to said workpiece-retaining parts; releasable clamping means for placing the aligned workpiece-retaining part and said wave-shaping part in pressure-tight relationship; and actuating means for said mounting member for moving the same to said positions.

7. Explosion-forming apparatus as claimed in claim 6, wherein said mounting member is rotatable about a fixed axis to move each workpiece-retaining part through four positions whereby the apparatus is vadapted for multi-station positioning of said workpiece-retaining parts to enable receipt preparation, forming .and removal of workpieces, to be carried out at respective stations in turn.

8. Apparatus as in claim `6 inclu-ding adjustable positioning means associated with said wave-shaping part for adjustably positioning an explosive charge Within said cavity.

9. Apparatus as in claim 6 wherein said clamping means is hydraulically operated.

10. Apparatus as in claim 6 including wedge means for engaging said clamping means to enable the latter to operate on said parts.

References Cited by the Examiner UNTED STATES PATENTS 2,030,803 2/ 1936 Temple 113-44 2,847,957 8/1958 Watter et al. 72-56 2,913,946 ll/ 1959 Ellrich -299 2,935,038 5/1960 Chatten 113-44 3,002,479 10/1961 Johansen et al. 72-412 3,024,592 3/1962 Leaman 29-421 3,044,430 7/ 1962 Zeigler 72-56 3,136,049 6/ 1964 Throner et al. 113-44 3,188,844 6/1965 Schwinghamer 72-56 `3,195,334 7/1965 Filler 72-56 3,200,626 8/1965 lCallender 72-56 CHARLES W. LANHAM, Primary Examiner.

R. I. HERBST, Assistant Examiner. 

1. AN EXPLOSION-FORMING APPARATUS FOR PERFORMING A FORMING OPERATION ON A WORKPIECE, COMPRISING A PRESSUREPULSE-SHAPING PART, SAID PULSE-SHAPING PART BEING ARRANGED TO FACE UPWARDLY SO AS TO RETAIN LIQUID FOR PULSE TRANSMITTING PURPOSES, A WORKPIECE-RETAINING PART, SAID WORKPIECERETAINING PART BEING ARRANGED FOR SUBSTANTIALLY PRESSURETIGHT CONNECTION TO SAID PULSE-SHAPING PART, AN EXPLOSIVEPOSITIONING MEANS ASSOCIATED WITH SAID PULSE-SHAPING PART, 